Per Russian telegram
Unconfirmed 40 dead
I suspect the numbers will rise sharply. From what i read around 100 people have been evacuated. An unknown number fled to the roof of the building and rescuers are working do save those. In the video from inside the hall there are at least several hundreds of people. The building is on fire. So things probably are rather grim.
It`s probably even worse than i thought. The concert was sold out. Depending on the configuration of the venue that means there were between around 2000 and 7000 tickets sold. From the videos i found Picnic seem to be really big in Russia and often play even larger venues. So the number of people in the hall may be closer to the upper end of that range